The present disclosure relates to a converter circuit and a method of driving the same, and more particularly, to a converter circuit for converting an output value of a sensing device such as a pixel circuit of an image sensor, detecting a different output value for each interval, and reducing noise occurring during the detection operation and a method of driving the same.
In an image sensor, a 4T pixel structure (e.g., a 4-transistor pinned-photodiode pixel) generates two output signals according to temporal timing. One is a reset voltage (i.e., an initial value) of a photo diode and the other is a signal voltage (i.e., a final value of a photo diode). Accordingly, a brightness value of light incident to the image sensor may be measured by detecting a difference between the initial value and the final value.
A related art Correlated Double Sampling (CDS) circuit may effectively measure the brightness value by using a difference between pixel output values. However, the image sensor of the 4T pixel structure is affected by a significant amount of noise, which is added or accumulated on the initial value and the final value. In this case, even when a low-frequency noise is removed through an analog CDS processing, the analog CDS processing may amplify a high-frequency noise.
Since the noise has a negative effect on a dynamic range of a photodiode pixel array, it needs to be reduced.